Adhesive wear between relatively movable parts made by powder metallurgy has remained a persistant problem in spite of prior art attempts to produce parts which contain a solid lubricant. The problem of adhesive wear occurs, for example, in connection with powdered metal engine parts, such as between valve guides and valve stems and between valve seat inserts and valve seat faces operating at high temperatures often in excess of 500.degree. F. It is particularly severe in heavy duty and natural gas engines. As diesel engines go to higher combustion peak pressures, the adhesive wear condition will be even more aggravated.
U.S. Pat. No. 4,274,875 discloses one prior art proposal for making a pre-lubricant powdered metal part such as a valve seat insert. As disclosed in the patent, powdered mica is included in a metal powder mixture prior to compacting and sintering the compact. Other conventional additives that have been proposed include molybdenum disulfide, bismuth, tin, lead, copper and phosphorus.
U.S. Pat. No. 4,569,693 discloses the addition of up to 0.5% by weight of finely divided extraneous metal oxides such as amorphous pyrogenic silica (Si O.sub.2), amorphous alumina, titanium dioxide, talc (hydrated magnesium silicate) or magnesium oxide and combinations thereof to powdered tantalum or niobium to improve the free flowability of the powdered metal before compacting and sintering the powdered mixture into electrical anodes.
U.S. Pat. No. 4,154,609 discloses the addition of from about 0.01 to about 10% by weight of at least one organic lubricant selected from sulfides, selenides and tellurides of a member of sub-groups V and VI of the periodic table as an inorganic lubricant for making molded anodes.
Although heretofore used in small amounts to improve flowability of powdered metal, no one prior to the present invention recognized the marked effect that the addition of greater amounts of powdered hydrated magnesium silicate (talc) would have in reducing seizing and scuffing of powdered metal parts such as valve seat inserts and valve guides operating at high temperatures in internal combustion engines.